1. Field of the Invention
The present invention relates to a solid-state imaging device integratedly having a microlens formed of a transparent resin or the like for the use of an image input device such as a movie camera device, a still camera, a facsimile machine and a wordprocessor.
2. Description of the Prior Art
FIG. 8 shows a known solid-state imaging device. This solid-state imaging device comprises a substrate 11, photodiodes 12, . . . as pixels formed in a top portion of the substrate 11, and microlenses 13, . . . formed of a transparent resin above the photodiodes 12, . . . A light is converged on the photodiode 12 through the microlens 13, whereby a photosensitivity of the device is improved. The reference numerals 16, . . . denote registers constituting CCDs (charge coupled devices), and a shaded portion indicated by the reference numeral 17 denotes a smoothing layer for smoothing a top surface of the substrate 11, which is rugged because of the photodiodes 12, . . . , the registers 16, . . . and the like formed thereon.
As the above microlens 13, a strip-shaped microlens 14 (FIG. 9a) and a rectangular microlens 15 (FIG. 9b) are well known. These microlenses 14 and 15 are each formed in the following way. First, as shown in FIGS. 10a and 10b, a lengthy strip pattern 14a or a rectangular pattern 15a is formed of a resin or a resist on the substrate 11 by photo-etching or the like, after the rugged top surface of the substrate 11 due to the photodiode, the register and the like is smoothed by the smoothing layer. Then, the lengthy strip pattern 14a or the rectangular pattern 15a is softened by heating or the like to make a convex curved surface by surface tension.
As illustrated in FIG. 11, an arranged pitch of the microlenses 15 is determined in accordance with the positional relationship between the microlenses 15 and the corresponding photodiodes 12. For improving the photosensitivity of the solid-state imaging device, a microlens should be made rectangular in order to have the largest possible area and the smallest possible gaps from the adjacent microlenses. Additionally, in the case of the rectangular microlens 15 having a curvature over all the directions of an upper surface thereof, the light incident from all the directions can be converged. In the case of the strip-shaped microlens 14, however, only a portion of the light incident from all the directions can be converged due to the shape thereof, resulting in a slightly lower photosensitivity than that of the rectangular microlens 15.
As shown in FIGS. 11 and 12, the rectangular microlens 15 has different widths in a longitudinal direction ("a" direction) and in a transverse direction ("b" direction) although having the same height H. Accordingly, the microlens 15 has different curvatures in the "a" and the "b" directions. In the case that the width W in the "a" direction is larger than the width W in the "b" direction, if the width W in the "a" direction is suitable to obtain a good light convergence (FIG. 13a), the width W in the "b" direction is short enough to obtain a poor light convergence (FIG. 13b). In consequence, the light convergence and the photosensitivity cannot be enhanced to a sufficiently high level in the conventional solid-state imaging device.